I personally think that Shinki is more powerful than Hecatia, though her win wouldn't be an easy one by any margin. The fact that Hecatia has the three most prominent hells under her sway (aside from any lesser ones) proves she's up there in the high echelons, but Shinki is greater as a creation god than Hecatia.
Besides, when it comes to Alice you just don't piss Shinki off... as a certain shrine maiden came to realize.
Hecatia is already stated by ZUN in Strange Creators of Outer World vol 1, to be the most powerful character in Touhou. Shinki also hasn't even been confirmed canon in the windows era touhou games nor has she made any appearances in anything official. So it's hard to say a character that technically doesn't even exist anymore is stronger than one ZUN himself said is the strongest of them all.
A bunch happened after this, but she failed to acquire Makai's Hell.Hecatia had enough power to conquer four Hells, butBy the way, I'm sorry, but could you exchange this money for me?The Earth
The Moon
The OtherworldsIn the present, these three worlds' Hells are ruled by Hecatia, but...the world she chose as her fourth was problematic.Long ago, there was one more world whose Hell she wanted control over.I wonder if we even have one... Well, I think we have enough help anyway.Give you Makai's Hell...? Goodness...This is an unattended counter, but I don't have any small change...Huh... You're refusing my request?Then I'll have to use force—
